STPM - Experiment 5

Experiment 5

Title: Volumetric Analysis – stoichiometry

Purpose: To determine the exact concentration of a monobasic acid, HX (KA1)

Materials and apparatus:

1.     Volumetric flask and stopper (250cm3)

2.     Electric balance ±0.01 g

3.     Pipette and pipette filler (25cm3)

4.     Volumetric flask and stopper (100cm3)

5.     Burettes (50cm3)

6.     Retort stand and clamp

7.     White tile

8.     Wash  bottle filled with distilled water

9.     Spatula

10.                        Titration flasks

11.                        Glass rod

12.                        Filter funnel

13.                        Beaker (80cm3)

14.                        Beaker (250cm3)

15.                        KA1 (monobasic acid, HX)

16.                        Methyl orange as indicator

17.                        Solid sodium carbonate

18.                        Distilled water

Theory:

To determine the exact concentration of a monobasic acid, HX,a standard base solution is prepared. Then, a certain amount of standard base solution is titrated with the monobasic acid. This is an acid-base titration. The equation for the reaction is

 Na₂CO₃(aq) + 2HX(aq) → 2NaX(aq) + H₂O(l) + CO₂(g)

Procedure:

1.     Weight accurately about 13.20-13.50g of solid sodium carbonate in a small beaker. Dissolve this in the beaker. Transfer the solution and washing into a 250cm3 standard flask and make up to the mark with distilled water. Shake well.

2.     Pipette 25.0 cm3 of the standard solution of sodium carbonate into a conical flask. Add two or three drops of methyl orange indicator and titre this solution with KA1. Readings are recorded in the table. The titration is repeated three times to achieve accurate results.

Results:

Titration number	Rough	Accurate
		1	2	3
Final reading/cm3
Initial reading/cm3
Volume of KA1/cm3

Mass of beaker + sodium carbonate= _________________

Mass of empty beaker                       = _________________

Mass of sodium carbonate               = _________________

Calculation:

1.     25.0 cm³ of standard solution of sodium carbonate required __________ of KA1 for complete reaction.

2.     Average titre value =

3.     Calculate the concentration of sodium carbonate.

4.     Calculate the concentration of the monobasic acid, HX in KA1.

Experiment 13 - STPM

Topic: Electrochemistry – Faraday’s laws

Purpose: To determine the value of Avogadro’s constant by the electrolysis procedure

Materials:
Copper(II) sulphate solution, propanone, 2 pieces of copper plates, 5 connecting wire with crocodiles clips, ammeter, rheostat, switch, 4 dry cells, stop watch, hair dryer, electric balance, wash bottle with distilled water, sand paper, one 250cm3 beaker, one 100cm3 measuring cylinder.

Procedures:
1.    100cm3 of copper(II) sulphate solution is measured using measuring cylinder, then it is poured into a beaker.
2.    2 copper plates are cleaned with sand papers and washed with distilled water before  dried  by hair dryer.
3.    Then, the 2 copper plates were labeled and weighed with electric balance. The mass was recorded in the table below.
4.    The circuit is set up as shown in the diagram.
5.    The circuit is switched on at the same time the stop watch is started.
6.    The rheostat is adjusted so that the current is fixed at 0.5A.
7.    Electrolysis is continued for 30 minutes.
8.    The circuit is switched off and the copper plates are taken out.
9.    The two copper plates are dipped into the distilled water and stirred slightly. For the anode copper, it is rubbed with cloth before wash.
10.    Then, two copper plates are dipped into 100cm3 of propanone and are dried using hair dryer.
11.    The copper plates are weighted with electric balance and the mass is recorded in the table.

Results:
                                       Anode    Cathode
Initial mass/g       
Final mass/g       
Difference in mass/g   
   
 Current= _____________

Time taken= _________________

Spotted topics for Paper 3 2010

Below are some spotted topics/experiment for Paper 3. Again, there is no guarantee that the experiment listed below will come out. Anyway, just try your best to study. Good luck to you.

1. Experiment about naphthalene: to determine the melting point and freezing points of naphthalene

2. Group 17: to investigate the chemical properties of Group 17 elements

3. Period 3: to investigate the properties of oxides of elements in Period 3

4. Salts: to construct an ionic equation for the formation of lead(II) chromate(VI)

5. Manufactured substances in industry: to compare the hardness of a pure metal and its alloy;  to compare the rate of rusting of iron, steel and stainless steel

6. Rate of reaction: factor of concentration, temperature and catalyst

7. Carbon compound: to investigate the elasticity of natural rubber and vulcanised rubber

8. Thermochemistry: Heat of precipation/displacement/combustion

9. Oxidation and reduction: U-tube/ displacement of halogen

10. Chemical bond: to compare the properties of ionic and covalent compounds

Please noticed that some topics are overlapped with Paper 2 tips. If any topics spotted for Paper 2 or 3 already come out in Paper 2, most probably it will not come in Paper 3 anymore. All the best to you.